Problem: Simplify the following expression: $y = \dfrac{-3x - 9}{5x + 4} \div \dfrac{1}{4}$
Dividing by a number is the same as multiplying by its inverse. $y = \dfrac{-3x - 9}{5x + 4} \times \dfrac{4}{1}$ When multiplying fractions, we multiply the numerators and the denominators. $y = \dfrac{(-3x - 9) \times 4} {(5x + 4) \times 1}$ $y = \dfrac{-12x - 36}{5x + 4}$